[PATCH] Add extended mnemonics for bctar. Fix setting of 'at' branch hints.

[Alan Modra]

On Wed, Apr 03, 2019 at 03:54:56PM -0500, Peter Bergner wrote:
> Anton complained that the bctar instruction was missing extended mnemonics
> to make reading disassembly more readable.  In the process of adding that
> support, I noticed that we were not correctly setting 'at' branch hints
> for many branches.  Instead, we were incorrectly setting the 1-bit 'y'
> branch hint, which wasn't correct on anything POWER4 and later.
> 
> The patch below adds the missing bctar extended mnemonics as well as
> now correctly setting and extracting 'at' branch hints.  The patch
> flagged some illegal tests within the a2.[ds] tests, so I fixed those
> to use legal operand values.
> 
> This passed testing with no errors.  I plan on committing this tomorrow.

So I wrote another testcase to check all the possible BO bits with
bc, bcctr, bclr and bctar, and noticed we have some problems remaining
with disassembly of insns using 'y' hints.  I'll commit the testcase
and fixes after your patch goes in.

-- 
Alan Modra
Australia Development Lab, IBM